This invention relates to valves for protection of rigid piping elements from damage due to freezing.
Local plumbing codes often require installation of a backflow preventer and/or an anti-siphon pressure vacuum breaker at outlets to exterior piping or hoses, e.g. lawn sprinkler systems, to prevent backflow of contaminated water into a potable water supply. When these piping elements are installed outdoors, there is a risk of damage in areas subject to conditions of below freezing temperatures, in particular where freezing is not normally expected and a sprinkler system is not winterized, at the end of a growing season before a sprinkler system has been drained and winterized, or where a sprinkler system is turned on too early in the spring and a late freeze occurs.
Piping elements such as pressure vacuum breakers, backflow preventers and the like often have a body formed of bronze or other rigid material. In conditions of freezing temperature, water inside the rigid body expands as it freezes, often to a degree sufficient to cause the rigid body to split, thus requiring replacement or repair at considerable cost and inconvenience.
It has also been known to construct pressure vacuum breakers, backflow preventers and the like with a bronze body incorporating plastic elements to cushion the rigid body during freezing conditions. As a result, the plastic elements may be damaged or destroyed by expansion of water with freezing, but these destructible elements act to protect the rigid body, thus reducing the cost, but not eliminating the nuisance, of the required repair and/or replacement of the plastic elements.